GENERAL PHYSIOLOGY OF NERVE-TISSUE. 91 



in a very complex manner. In a subsequent chapter the anatomic arrange- 

 ment of their constituent parts will be detailed. 



The Peripheral Organs of the Nerve System. These consist of the 

 cranial and spinal nerves and the sympathetic ganglia. Each nerve 

 consists of a variable number of nerve-fibers united into firm bundles by 

 connective tissue which supports blood-vessels and lymphatics. The bundles 

 are technically known as nerve-trunks or nerves. 



The nerve-trunks connect the brain and cord with all the remaining 

 structures of the body. Each nerve is invested by a thick layer of lamel- 

 lated connective tissue, known as the epineurium. A transverse section of a 

 nerve shows (see Fig. 45), that it is made up of a number of small bundles of 



FIG. 45. TRANSVERSE SECTION OF A NERVE (MEDIAN), ep. Epineurium. 

 pe. Perineurium. ed. Endoneurium. (Landois and Stirling.} 



fibers, each of which possesses a separate investment of connective tissue 

 the perineurium. Within this membrane the nerve-fibers are supported by 

 a fine stroma the endoneurium. After pursuing a longer or shorter course, 

 the nerve-trunk gives off branches, which interlace very freely with neigh- 

 boring branches, forming plexuses, the fibers of which are distributed to 

 associated organs and regions of the body. From their origin to their 

 termination, however, nerve-fibers retain their individuality, and never be- 

 come blended with adjoining fibers. 



As nerves pass from their origin to their peripheral terminations, they 

 give off a number of branches, each of which becomes invested with a 

 lamellated sheath an offshoot from that investing the parent trunk. This 

 division of nerve-bundles and sheath continues throughout all the branchings 

 down to the ultimate nerve-fibers, each of which is surrounded by a sheath 

 of its own, consisting of a single layer of endothelial cells. This delicate 

 transparent membrane, the sheath of Henle, is separated from the nerve- 

 fiber by a considerable space, in which is contained lymph destined for the 

 nutrition of the fiber. Near their ultimate terminations the nerve-fibers 



